package cn.cqs.redisitem.utils;

import java.util.BitSet;

/**
 * 简单bloomFilter
 */

public class SimpleBloomFilter {
    private static final int DEFAULT_SIZE = 2 << 24;
    private static final int[] seeds = new int[]{7, 11, 13, 31, 37, 61};
    private BitSet bits = new BitSet(DEFAULT_SIZE);
    private SimpleHash[] func = new SimpleHash[seeds.length];

    public SimpleBloomFilter() {
        //创建多个哈希函数
        for (int i = 0; i < seeds.length; i++) {
            func[i] = new SimpleHash(DEFAULT_SIZE, seeds[i]);
        }
    }

    /**
     * 添加元素到布隆过滤器中
     *
     * @param value
     */
    public void put(String value) {
        for (SimpleHash f : func) {
            bits.set(f.hash(value), true);
        }
    }

    /**
     * 判断布隆过滤器中是否包含指定元素
     *
     * @param value
     * @return
     */
    public boolean mightContain(String value) {
        if (value == null) {
            return false;
        }
        boolean ret = true;
        for (SimpleHash f : func) {
            ret = ret && bits.get(f.hash(value));
        }
        return ret;
    }

    class SimpleHash{
        private int cap;
        private int seed;

       public SimpleHash(int cap, int seed) {
           this.cap = cap;
           this.seed = seed;
       }

       public int hash(String value) {
           int result=0;
           int len=value.length();
           for (int i=0;i<len;i++) {
               result = seed * result + value.charAt(i);
           }
           return (cap-1)&result;
       }
   }

}
